PVDF / rGO / Fe (II) composite membrane as electro-Fenton cathode, preparation method, application and membrane filtration reactor

Abstract

The invention relates to a PVDF / rGO / Fe (II) composite membrane serving as an electro-Fenton cathode, a preparation method, application and a membrane filtration reactor. The preparation method comprises the following steps: firstly, preparing a PVDF membrane by adopting a phase inversion method, and covering the surface of the PVDF membrane with reduced graphene oxide by adopting a suction filtration method to obtain a PVDF / rGO double-layer membrane; then, dispersing the siderite powder in an organic solvent, adding a pore-foaming agent and PVDF, and heating and stirring to prepare a uniform membrane casting solution; and finally, coating the surface of the PVDF / rGO double-layer membrane with the membrane casting solution to obtain the PVDF / rGO / Fe (II) composite membrane. The composite membrane is used as an electro-Fenton cathode to be applied to a filtering system or a membrane bioreactor of organic pollutants and bacteria, has excellent anti-pollution effect and bacteria killing capability, can remarkably inhibit the formation of a biological membrane on the surface of the membrane, and has wide application prospect in the aspect of membrane pollution resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation in water treatment, and in particular relates to a PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode, a preparation method, an application, and a membrane filtration reactor. Background Art

[0002] With the increasing demand for water treatment, the membrane separation industry has developed rapidly and has become an important new force in my country's water treatment field. Organic membranes in membrane separation materials, such as polyvinylidene fluoride (PVDF) membranes, are the most widely used in industry, but this type of material is easily contaminated due to its strong hydrophobicity. Membrane pollution often leads to an increase in transmembrane pressure difference and a decrease in filtration flux, increasing energy consumption, feed pressure and membrane cleaning frequency, shortening the service life of the membrane, and thus increasing the operation and maintenance costs of the system. Membrane bioreactor (MBR), as a combination of membrane filtration technology and sewage biological treatment process, is also deeply troubled by membrane pollution problems. Membrane pollution not only leads to an increase in the frequency of MBR membrane cleaning, but the irreversible pollution on the membrane will also accelerate the aging of the membrane components, thereby further increasing the operating cost. Therefore, research on membrane pollution control methods has received widespread attention in the industry.

[0003] Traditional membrane pollution control technologies mainly include adding grid / screen interception units or chemical cleaning, but such methods will not only increase energy consumption and drug consumption, but also shorten the service life of membrane materials. Domestic and foreign scholars have found that the use of membrane modification methods to give membrane materials special anti-pollution properties is a direct and effective means to inhibit membrane pollution. Common membrane modification methods mainly obtain modified membranes by introducing antibacterial materials or hydrophilic substances on the surface of membrane materials. However, the anti-pollution performance of the above-mentioned modified membranes will gradually weaken with the continuous release of surface antibacterial or hydrophilic materials. Not only are they poor in durability and stability, but the released materials will also inhibit the metabolic activity of functional microorganisms in the system and reduce the water treatment effect. Therefore, the development of environmentally friendly and highly sustainable anti-pollution modified membranes based on membrane modification methods, which have both antibacterial and in-situ degradation properties of membrane pollutants, has become a key technical issue that urgently needs to be broken through in the field of membrane pollution control.

[0004] As a typical advanced oxidation technology, the electro-Fenton technology uses electrochemical reactions to continuously produce H2O2 at the cathode, which reacts with Fe(Ⅱ) in the solution to generate a large amount of highly oxidizing ‧OH; the generated ‧OH can effectively degrade organic pollutants in water and inactivate bacteria; the associated Fe(Ⅲ) can be reduced to Fe(Ⅱ) at the cathode, thereby achieving continuous regeneration of Fe(Ⅱ). The membrane electrode electro-Fenton technology constructed with a modified membrane as an electrocatalytic cathode is an efficient and environmentally friendly membrane pollution control technology. This technology can produce H2O2 on the membrane surface. The ‧OH generated by the reaction of H2O2 and Fe(Ⅱ) can directly inactivate bacteria on the membrane surface and degrade membrane pollutants, effectively reducing membrane pollution. However, the Fe(Ⅱ) in the currently reported membrane electrode electro-Fenton system mainly comes from external addition or release from pure Fe anode, and it is difficult to ensure that ‧OH is only produced on the surface of the modified membrane, which not only reduces the inhibition efficiency of ‧OH on membrane pollution, but also has an adverse effect on functional microorganisms. Summary of the invention

[0005] In view of the above problems existing in the prior art, the present invention provides a PVDF / rGO / Fe(Ⅱ) composite membrane as an electro-Fenton cathode, a preparation method, an application, and a membrane filtration reactor, which has excellent anti-pollution and antibacterial effects and can achieve efficient inhibition of membrane pollution.

[0006] To achieve the above object, the technical solution provided by the present invention is as follows:

[0007] In a first aspect, the present application provides a PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode, comprising a substrate layer, an electro-Fenton active layer, and a conductive layer arranged between the substrate layer and the electro-Fenton active layer, wherein the substrate layer comprises a polyvinylidene fluoride membrane, and the electro-Fenton active layer comprises a polyvinylidene fluoride membrane doped with siderite.

[0008] Optionally, the pore size of the electro-Fenton active layer is larger than that of the substrate layer.

[0009] Optionally, the conductive layer is a reduced graphene oxide film.

[0010] Optionally, the polyvinylidene fluoride membrane is prepared by a phase inversion method, and the pore size of the polyvinylidene fluoride membrane is 0.1-0.3 μm and the thickness is 100-200 μm.

[0011] In a second aspect, the present application further provides a method for preparing the PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode as described in the first aspect, comprising the following steps:

[0012] 1) Dispersing reduced graphene oxide in deionized water, using a base membrane to filter the reduced graphene oxide dispersion by suction, so that the reduced graphene oxide is covered on the base membrane, and then drying to obtain a PVDF / rGO double-layer membrane;

[0013] 2) ultrasonically dispersing siderite powder in an organic solvent, adding a porogen and polyvinylidene fluoride, and heating and stirring to obtain a film casting solution;

[0014] 3) coating the vacuum degassing casting solution on one side of the reduced graphene oxide of the PVDF / rGO double-layer membrane, letting it stand and then immersing it in a coagulation bath to coagulate into a membrane, taking it out after the membrane falls off and soaking it in water, and obtaining the PVDF / rGO / Fe(Ⅱ) composite membrane after drying.

[0015] Optionally, the number of reduced graphene oxide layers is ≤5, and the amount of reduced graphene oxide added per unit area of ​​the substrate film is 2-10 g / m 2 .

[0016] Optionally, the reduced graphene oxide is dispersed in deionized water under ultrasonic action, and the ultrasonic time is 30-60 minutes.

[0017] Optionally, in step 2), the casting solution is prepared from the following components in parts by weight: 76-80 parts of organic solvent, 13-17 parts of polyvinylidene fluoride, 3-6 parts of porogen, and 2-3 parts of siderite powder.

[0018] Optionally, the particle size of the siderite powder is 20-60 μm.

[0019] Optionally, in step 3), the standing still is standing still in the air for 5-15 seconds.

[0020] Optionally, in step 3), after the membrane is detached, the membrane is taken out and soaked in water for 24-48 hours.

[0021] Optionally, in step 3), the coating thickness of the casting solution is 100-200 μm.

[0022] Optionally, in step 1), the drying condition is drying at 40-50° C. for 4-5 h.

[0023] Optionally, in step 3), the drying is carried out by natural air drying.

[0024] In a third aspect, the present application also provides an application of the PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode described in the first aspect in inactivating bacteria on the membrane surface and degrading organic matter on the membrane surface.

[0025] In a fourth aspect, the present application also provides a membrane filtration reactor, comprising the PVDF / rGO / Fe(Ⅱ) composite membrane as the electro-Fenton cathode described in the first aspect, wherein the PVDF / rGO / Fe(Ⅱ) composite membrane as the electro-Fenton cathode is connected to the negative electrode of a DC power supply as the electro-Fenton cathode, and electro-Fenton anode materials are arranged in parallel on both sides of the electro-Fenton cathode, and the electro-Fenton anode materials are connected to the positive electrode of the power supply.

[0026] The PVDF / rGO / Fe(Ⅱ) composite membrane as an electro-Fenton cathode of the present invention can be used in an organic pollutant and / or bacterial filtration device or a membrane bioreactor (MBR), and can achieve inactivation of bacteria on the surface of the composite membrane and degradation of organic pollutants on the membrane surface under certain current density conditions, thereby inhibiting membrane fouling. The method of using the PVDF / rGO / Fe(Ⅱ) composite membrane of the present invention to achieve resistance to organic and bacterial pollution in a membrane filtration reactor under certain current density conditions and to resist membrane fouling in the long-term operation of an MBR is as follows:

[0027] A membrane filtration reactor device was constructed. The PVDF / rGO / Fe(Ⅱ) composite membrane was fixed on a flat membrane assembly and installed in a membrane filtration reactor. It was connected to the negative electrode of a DC power supply as an electro-Fenton cathode. An electro-Fenton anode material with the same area as the composite membrane was installed on both sides of the flat membrane assembly. The positive and negative electrodes were parallel to each other with a distance of 0.5-1.5 cm. The anode material was connected to the positive electrode of the power supply. A stirring device was set under the electrode at the bottom of the reactor. The constant current density was set to 0.2-0.4 mA / cm 2 .

[0028] When an organic pollutant solution is prepared in a reactor to form a pollutant filtration system, the pollutant solution is filtered through the PVDF / rGO / Fe(Ⅱ) composite membrane, and the filtrate flows out from the outlet of the membrane assembly. The PVDF / rGO / Fe(Ⅱ) composite membrane can inhibit organic pollution on the membrane surface under constant current density and continuous stirring conditions; when a bacterial suspension is prepared in a reactor to form a bacterial filtration system, the PVDF / rGO / Fe(Ⅱ) composite membrane can inactivate bacteria on the membrane surface under constant current density and continuous stirring conditions; when a mud-water mixture is added into the reactor to form an MBR, the PVDF / rGO / Fe(Ⅱ) composite membrane can control membrane pollution under constant current density and continuous stirring conditions.

[0029] Optionally, the organic pollutants include proteins represented by bovine serum albumin, polysaccharides represented by sodium alginate and humus represented by humic acid; the bacteria include Gram-negative bacteria represented by Escherichia coli and Gram-positive bacteria represented by Staphylococcus aureus; and the sludge in the mud-water mixture includes anaerobic ammonia oxidation sludge, aerobic activated sludge and anaerobic digestion sludge.

[0030] The PVDF / rGO / Fe(Ⅱ) composite membrane of the present invention as an electro-Fenton cathode can generate H2O2 by reducing H2O and O2 on the membrane under constant low current density conditions, and then react with Fe(Ⅱ) dissolved from siderite particles on the membrane surface to generate non-selective and highly oxidizing ‧OH. ‧OH can effectively oxidize and decompose organic pollutants adhered to the membrane surface, inactivate bacteria attached to the membrane surface, delay the formation of biofilm, and thus inhibit membrane pollution.

[0031] In the present invention, the electro-Fenton active layer on the PVDF / rGO / Fe(Ⅱ) composite membrane is prepared by doping siderite whose main component is FeCO3. Siderite is not only cheap and easy to obtain, but also can slowly release Fe(Ⅱ) during the membrane filtration process, ensuring that ‧OH is generated in situ on the membrane surface, thereby improving the utilization efficiency of ‧OH in inhibiting membrane pollution and avoiding the adverse effects of ‧OH on the functional microorganisms in the membrane filtration system. Fe(Ⅲ) associated with the electro-Fenton reaction can be reduced to Fe(Ⅱ) on the cathode membrane surface, thereby ensuring the sustainability of the anti-membrane pollution process.

[0032] The rGO conductive layer in the middle of the composite membrane solves the problem of poor conductivity of PVDF polymer materials. rGO has extremely strong conductivity. H2O and O2 on the membrane surface can be reduced to H2O2 by electrons from the electro-Fenton cathode on the rGO conductive layer, and quickly react with Fe(Ⅱ) in the active layer, further ensuring that ‧OH is generated in situ on the membrane surface. In addition, the separation of the electro-Fenton active layer and the substrate layer can prevent ‧OH from directly contacting the substrate layer and oxidizing the membrane material; the rGO conductive layer further separates ‧OH from the substrate layer and protects the substrate layer; the membrane pores of the electro-Fenton active layer are larger than those of the substrate layer, avoiding the decrease in the membrane permeability caused by the coverage of the electro-Fenton active layer. The PVDF / rGO / Fe(Ⅱ) composite membrane provided by the present invention has high hydrophilicity, strong water permeability, and good electro-Fenton activity. It can effectively reduce the membrane pore blockage caused by organic pollutants such as proteins represented by bovine serum albumin, polysaccharides represented by sodium alginate, and humus represented by humic acid at a constant current density, and has a good killing effect on Gram-negative bacteria represented by Escherichia coli and Gram-positive bacteria represented by Staphylococcus aureus. It can significantly inhibit the formation of biofilm on the membrane surface, has excellent simultaneous anti-pollution and antibacterial effects, and shows great anti-pollution application potential in MBR.

[0033] Compared with the prior art, the present invention has at least the following beneficial effects:

[0034] 1) The PVDF / rGO / Fe(Ⅱ) composite membrane provided by the present invention as an electro-Fenton cathode is more hydrophilic than the traditional PVDF modified membrane and has significant electro-Fenton anti-fouling performance; the siderite in the electro-Fenton active layer can gradually release Fe(Ⅱ) during the membrane filtration process, directly reacting with the electrochemically generated H2O2 to generate ‧OH in situ on the surface of the composite membrane, thereby improving the utilization efficiency of ‧OH while avoiding its adverse effects on functional microorganisms; it has good simultaneous anti-fouling and antibacterial effects, can effectively reduce membrane pollution and delay the rate of membrane flux decline.

[0035] 2) The PVDF / rGO / Fe(Ⅱ) composite membrane provided by the present invention as an electro-Fenton cathode has stronger conductivity and stability. The middle rGO conductive layer gives the composite membrane excellent conductivity, accelerates the in-situ generation of H2O2 on the membrane surface, and isolates the substrate layer from the electro-Fenton active layer, avoiding direct oxidation of the substrate layer by ‧OH, thereby ensuring the durability and stability of the membrane material.

[0036] 3) The method for preparing PVDF / rGO / Fe(Ⅱ) composite membrane of the present invention is a phase transformation method combined with a blending modification method. The layers of the membrane are tightly bonded and are not easily peeled off during long-term filtration and anti-pollution processes. The siderite in the electro-Fenton active layer is not easily lost with the water flow and dissolves slowly, ensuring that the composite membrane has a long anti-pollution service life.

[0037] 4) The method for preparing PVDF / rGO / Fe(II) composite membrane of the present invention is simple and easy to operate. Siderite as an electro-Fenton active material has low cost and mild reaction conditions. It can be widely used in the preparation of modified membrane materials as electro-Fenton cathodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a diagram of the anti-pollution mechanism of the PVDF / rGO / Fe(Ⅱ) composite membrane prepared in Example 1;

[0039] Figure 2 The electron paramagnetic resonance (EPR) spectrum of ‧OH detected by DMPO spin trapping of the PVDF / rGO / Fe(Ⅱ) composite membrane prepared in Example 1 in Na2SO4 solution and deionized water;

[0040] Figure 3 The PVDF / rGO / Fe(Ⅱ) composite membrane prepared in Example 1 and the PVDF membrane were used to filter bovine serum albumin (BSA) in a membrane filtration reactor under the conditions of electro-Fenton reaction and non-electro-Fenton reaction. Figure 3 a) Sodium alginate (SA) Figure 3 b) and humic acid (HA) ( Figure 3 c) Curve of relative flux of solution changing with time;

[0041] Figure 4 The inactivation performance of the PVDF / rGO / Fe(Ⅱ) composite membrane and the PVDF membrane prepared in Example 1 on Escherichia coli and Staphylococcus aureus in a membrane filtration reactor under the conditions where the electro-Fenton reaction occurs and does not occur;

[0042] Figure 5 When the PVDF / rGO / Fe(Ⅱ) composite membrane prepared in Example 1 undergoes an electro-Fenton reaction ( Figure 5 a and 5c) with PVDF membrane ( Figure 5 b and 5d) Filtration of Escherichia coli ( Figure 5 a and 5b) and Staphylococcus aureus ( Figure 5 c and 5d) Bacterial morphology on the surface of the rear membrane;

[0043] Figure 6 The change of transmembrane pressure difference between the PVDF / rGO / Fe(II) composite membrane and the PVDF membrane used as the electro-Fenton cathode prepared in Example 1 in the MBR during 190 days of operation. DETAILED DESCRIPTION

[0044] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0045] The experimental methods used in the embodiments of the present invention are conventional methods unless otherwise specified.

[0046] The reagents and materials used in this example can all be purchased conventionally. The quantitative experiments involved in the examples were repeated at least three times, and the results were averaged.

[0047] Raw materials: Single-layer rGO: particle size is 0.2-10μm; Few-layer rGO: number of layers is 3-5, particle size is 5-50μm.

[0048] Example 1

[0049] A polyvinylidene fluoride membrane (PVDF membrane) with a pore size of 0.2 μm and a thickness of 150 μm was prepared by a phase inversion method. A single layer of reduced graphene oxide (rGO) was weighed according to 8 g of reduced graphene oxide per square meter of PVDF, added to deionized water and dispersed under ultrasound for 45 min, and the rGO dispersion was suction filtered using a PVDF membrane to cover the membrane surface with rGO. The membrane was dried in an oven at 45°C for 5 h to obtain a PVDF / rGO double-layer membrane. 3 g of siderite powder with a particle size of 20-40 μm (previously dried in an oven at 70°C for 12 h) was ultrasonically dispersed in 78 g of N, N-dimethylacetamide, 5 g of dried polyvinyl pyrrolidone porogen and 14 g of dried polyvinylidene fluoride (PVDF) were added, and the mixture was heated and stirred at 85°C for 18 h to prepare a uniform casting solution. The casting solution was degassed in a vacuum drying oven for 5 h later, the casting liquid was coated on the rGO side of the above-mentioned PVDF / rGO double-layer membrane by a scraper on a scraper machine, and the coating thickness was 150 μm to form a liquid film; the PVDF / rGO double-layer membrane coated with the liquid film was allowed to stand in the air for 10 s and then immersed in a coagulation bath of deionized water to coagulate into a membrane. After the membrane fell off, it was taken out and soaked in deionized water for 36 h, and then naturally air-dried to obtain a PVDF / rGO / Fe(Ⅱ) composite membrane.

[0050] Figure 1 : is the anti-pollution mechanism diagram of the PVDF / rGO / Fe(Ⅱ) composite membrane prepared in this embodiment. The PVDF / rGO / Fe(Ⅱ) composite membrane is composed of a lower PVDF substrate layer, a middle rGO conductive layer and an upper electro-Fenton active layer. The electrons provided by the electro-Fenton cathode are conducted through the rGO conductive layer to reduce H2O and O2 to H2O2, and H2O2 reacts with Fe(Ⅱ) dissolved from siderite on the Fe(Ⅱ) active layer to generate ·OH, thereby degrading organic pollutants on the membrane surface and inactivating bacteria, thereby achieving the purpose of inhibiting membrane pollution.

[0051] Figure 2 The EPR diagram of ‧OH detected by DMPO spin capture in Na2SO4 solution and deionized water for the PVDF / rGO / Fe(Ⅱ) composite membrane prepared in this example. Figure 2 It can be seen that the PVDF / rGO / Fe(Ⅱ) composite membrane acts as an electro-Fenton cathode with a connectivity density of 0.3 mA / m 2 When the current was , a strong characteristic peak with an intensity ratio of 1:2:2:1 corresponding to DMPO-‧OH was observed in both Na2SO4 solution and deionized water, indicating that the H2O2 produced on the surface of the composite membrane was successfully converted into ‧OH, confirming the anti-fouling potential of the composite membrane.

[0052] The method of using the PVDF / rGO / Fe(II) composite membrane prepared in this embodiment as an electro-Fenton cathode to achieve resistance to organic pollution and antibacterial in a membrane filtration reactor and resistance to membrane pollution in long-term operation of an MBR under constant low current density conditions is as follows:

[0053] Construction of membrane filtration reactor: The PVDF / rGO / Fe(Ⅱ) composite membrane was fixed on a flat membrane assembly and installed in a membrane filtration reactor, which was connected to the negative electrode of a DC power supply as an electro-Fenton cathode. An iron mesh with the same area as the composite membrane was installed on both sides of the flat membrane assembly, with the positive and negative electrodes parallel to each other and a distance of 1 cm between them. The iron mesh was connected to the positive electrode of the power supply. A stirring device was set under the bottom electrode of the reactor. The constant current density was set to 0.3 mA / cm 2 .

[0054] BSA, SA and HA solutions were prepared in a reactor to form a pollutant filtration system. After the pollutant solution was filtered through the PVDF / rGO / Fe(Ⅱ) composite membrane, the filtrate flowed out from the outlet of the membrane assembly and was connected to a constant current for continuous stirring to examine the ability of the composite membrane to resist organic pollutants. Figure 3 The PVDF / rGO / Fe(Ⅱ) composite membrane prepared in this example and the PVDF membrane (same as the substrate material) were used to filter BSA in a membrane filtration reactor under the conditions of electro-Fenton reaction and without it. Figure 3 a) SA Figure 3 b) and HA ( Figure 3 c) Curve of the relative flux of the solution changing with time. The results show that after 120 min of filtration, the relative flux decrease rates of BSA, SA and HA solutions filtered by the composite membrane with electro-Fenton reaction were reduced by 7.3%, 14.4% and 4.7% respectively compared with the PVDF membrane, indicating that the composite membrane prepared in this example has good resistance to organic pollutants when used as an electro-Fenton cathode. In addition, the relative flux decrease rates of BSA, SA and HA solutions filtered by the composite membrane without electro-Fenton reaction were also significantly higher than those of the PVDF membrane, indicating that the water permeability and anti-pollutant adhesion properties of the composite membrane prepared in this example were also improved.

[0055] Escherichia coli and Staphylococcus aureus suspensions were prepared in the reactor to form a bacterial filtration system. After a constant current was connected and continuous stirring was performed, the antibacterial ability of the composite membrane was investigated. Figure 4The inactivation performance of the PVDF / rGO / Fe(Ⅱ) composite membrane and PVDF membrane prepared in this example on Escherichia coli and Staphylococcus aureus in a membrane filtration reactor under the conditions of and without the electro-Fenton reaction. The results showed that the PVDF membrane and the composite membrane without the electro-Fenton reaction had no antibacterial effect, and the composite membrane with the electro-Fenton reaction had an inactivation rate of 90.4% and 86.2% on Escherichia coli and Staphylococcus aureus, respectively, indicating that the composite membrane prepared in this example is non-toxic to microorganisms, but has a good antibacterial effect on both Gram-negative and Gram-positive bacteria when used as an electro-Fenton cathode.

[0056] Figure 5 When the PVDF / rGO / Fe(Ⅱ) composite membrane prepared in this example undergoes an electro-Fenton reaction ( Figure 5 a and 5c) with PVDF membrane ( Figure 5 b and 5d) Filtration of Escherichia coli ( Figure 5 a and 5b) and Staphylococcus aureus ( Figure 5 c and 5d) The bacterial morphology on the membrane surface. Figure 5 As shown, the cell structure of bacteria on the PVDF membrane is intact, while after the composite membrane undergoes an electro-Fenton reaction, the cell integrity of the bacteria on its surface is destroyed, causing the outflow of cell contents and leading to cell death. This proves that when the composite membrane prepared in this example is used as an electro-Fenton cathode, the ‧OH generated on the surface of the composite membrane achieves bacterial inactivation by destroying cell integrity.

[0057] The anaerobic ammonium oxidation sludge and water mixture was added into the reactor to form an MBR. After connecting a constant current, continuous stirring was performed to investigate the anti-pollution ability of the composite membrane during the long-term operation of the MBR. Figure 6 The change of transmembrane pressure difference between the PVDF / rGO / Fe(Ⅱ) composite membrane and the PVDF membrane prepared in this example as the electro-Fenton cathode in the MBR during 190 days of operation. The results show that after the start of the electro-Fenton reaction, the average fouling period of the composite membrane (31.4 d) is twice that of the PVDF membrane (15.7 d), indicating that the composite membrane prepared in this example degrades the adhered pollutants and inactivates the attached bacteria by producing ‧OH on its surface during the operation of the MBR, alleviates the formation of biofilm on the membrane surface and the blockage of membrane pores, and significantly prolongs the membrane fouling period.

[0058] Embodiment 2:

[0059] A PVDF membrane with a pore size of 0.15 μm and a thickness of 130 μm was prepared by a phase inversion method. Few-layer reduced graphene oxide (few-layer rGO) was weighed according to the amount of 6 g reduced graphene oxide per square meter of PVDF, added to deionized water and dispersed under ultrasound for 40 min, and the rGO dispersion was suction filtered using a PVDF membrane to cover the membrane surface with rGO. The membrane was dried in an oven at 42°C for 4.3 h to obtain a PVDF / rGO double-layer membrane. 2.7 g of siderite powder with a particle size of 20-30 μm (previously dried in an oven at 65°C for 10 h) was ultrasonically dispersed in 77.3 g of N, N-dimethylacetamide, 4 g of dried polyethylene glycol porogen and 16 g of dried PVDF were added, and the mixture was heated and stirred at 83°C for 16 h to prepare a uniform casting solution. The casting solution was degassed in a vacuum drying oven for 4 h later, the casting liquid was coated on the rGO side of the above-mentioned PVDF / rGO double-layer membrane by a scraper on a scraper machine, and the coating thickness was 120 μm to form a liquid film; the PVDF / rGO double-layer membrane coated with the liquid film was allowed to stand in the air for 8 s and then immersed in a coagulation bath of deionized water. After the membrane fell off, it was taken out and soaked in deionized water for 30 h, and then naturally air-dried to obtain a PVDF / rGO / Fe(Ⅱ) composite membrane.

[0060] The method of using the PVDF / rGO / Fe(II) composite membrane prepared in this embodiment as an electro-Fenton cathode to achieve resistance to organic pollution and antibacterial in a membrane filtration reactor and resistance to membrane pollution in long-term operation of an MBR under constant low current density conditions is as follows:

[0061] A membrane filtration reactor was constructed. The PVDF / rGO / Fe(Ⅱ) composite membrane was fixed on a flat membrane assembly and installed in the membrane filtration reactor. It was connected to the negative electrode of a DC power supply as an electro-Fenton cathode. Iron sheets with the same area as the composite membrane were installed on both sides of the flat membrane assembly. The positive and negative electrodes were parallel to each other with a distance of 0.5 cm between them. The iron sheets were connected to the positive electrode of the power supply. A stirring device was set under the bottom electrode of the reactor. The constant current density was set to 0.2 mA / cm 2 .

[0062] BSA, SA and HA solutions were prepared in the reactor to form a pollutant filtration system. After the pollutant solution was filtered through the PVDF / rGO / Fe(Ⅱ) composite membrane, the filtrate flowed out from the water outlet of the membrane assembly, and was connected to a constant current and continuously stirred to investigate the ability of the composite membrane to resist organic pollutants. The results showed that after 120 min of filtration, the relative flux reduction rates of BSA, SA and HA solutions filtered by the composite membrane with electro-Fenton reaction were reduced by 5.5%, 13.0% and 4.5% respectively compared with the PVDF membrane, indicating that the composite membrane prepared in this example has good resistance to organic pollutants when used as an electro-Fenton cathode. In addition, the relative flux reduction rates of BSA, SA and HA solutions filtered by the composite membrane without electro-Fenton reaction were also significantly higher than those of the PVDF membrane, indicating that the water permeability and anti-pollutant adhesion properties of the composite membrane prepared in this example were also improved.

[0063] Escherichia coli and Staphylococcus aureus suspensions were prepared in the reactor to form a bacterial filtration system, and then a constant current was connected and stirred continuously to examine the antibacterial ability of the composite membrane. The results showed that the PVDF membrane and the composite membrane without the electro-Fenton reaction had no antibacterial effect, and the composite membrane with the electro-Fenton reaction had an inactivation rate of 89.1% and 83.5% for Escherichia coli and Staphylococcus aureus, respectively, indicating that the composite membrane prepared in this example was non-toxic to microorganisms, but had a good antibacterial effect on both Gram-negative and Gram-positive bacteria when used as an electro-Fenton cathode.

[0064] The aerobic activated sludge and water mixture was added into the reactor to form an MBR, and a constant current was connected for continuous stirring to investigate the anti-pollution ability of the composite membrane during the long-term operation of the MBR. The results showed that after the start of the electro-Fenton reaction, the average pollution cycle of the composite membrane (29.6 d) was 1.9 times that of the PVDF membrane (15.4 d), indicating that the composite membrane prepared in this example degraded the adhered pollutants and inactivated the attached bacteria by generating ‧OH on its surface during the operation of the MBR, which alleviated the formation of biofilm on the membrane surface and the blockage of membrane pores, and significantly prolonged the membrane pollution cycle.

[0065] Embodiment 3:

[0066] The PVDF membrane with a pore size of 0.25 μm and a thickness of 170 μm was prepared by phase inversion method. 10 g / m 2The single layer of rGO of the PVDF membrane was ultrasonically dispersed in deionized water for 50 min, and the rGO dispersion was suction filtered using a PVDF membrane to cover the membrane surface with rGO, and the PVDF / rGO double-layer membrane was prepared after drying in an oven at 48°C for 4.8 h. 2.5 g of siderite powder with a particle size of 20-50 μm (preliminarily dried in an oven at 75°C for 14 h) was taken and ultrasonically dispersed in 80 g of N, N-dimethylacetamide, 4.5 g of dried hexadecyltrimethylammonium bromide porogen and 13 g of dried PVDF were added, and heated and stirred at 87°C for 14 h to prepare a uniform casting liquid. After the casting liquid was degassed in a vacuum drying oven for 3 h, the casting liquid was coated on the rGO side of the above-mentioned PVDF / rGO double-layer membrane with a scraper on a scraper, and the coating thickness was 170 μm to prepare a liquid film. The PVDF / rGO double-layer membrane coated with the liquid film was allowed to stand in air for 12 After s, it was immersed in a coagulation bath of deionized water. After the membrane fell off, it was taken out and soaked in deionized water for 42 h. After natural air drying, the PVDF / rGO / Fe(Ⅱ) composite membrane was obtained.

[0067] The method of using the PVDF / rGO / Fe(II) composite membrane prepared in this embodiment as an electro-Fenton cathode to achieve resistance to organic pollution and antibacterial in a membrane filtration reactor and resistance to membrane pollution in long-term operation of an MBR under constant low current density conditions is as follows:

[0068] A membrane filtration reactor device was constructed. The PVDF / rGO / Fe(Ⅱ) composite membrane was fixed on a flat membrane assembly and installed in a membrane filtration reactor. It was connected to the negative electrode of a DC power supply as an electro-Fenton cathode. An iron mesh with the same area as the composite membrane was installed on both sides of the flat membrane assembly. The positive and negative electrodes were parallel to each other with a distance of 1.5 cm. The iron mesh was connected to the positive electrode of the power supply. A stirring device was set under the bottom electrode of the reactor. The constant current density was set to 0.4 mA / cm 2 .

[0069] BSA, SA and HA solutions were prepared in the reactor to form a pollutant filtration system. After the pollutant solution was filtered through the PVDF / rGO / Fe(Ⅱ) composite membrane, the filtrate flowed out from the water outlet of the membrane assembly, and was connected to a constant current and continuously stirred to investigate the ability of the composite membrane to resist organic pollutants. The results showed that after 120 min of filtration, the relative flux reduction rates of BSA, SA and HA solutions filtered by the composite membrane with electro-Fenton reaction were reduced by 6.7%, 11.6% and 4.2% respectively compared with the PVDF membrane, indicating that the composite membrane prepared in this example has good resistance to organic pollutants when used as an electro-Fenton cathode. In addition, the relative flux reduction rates of BSA, SA and HA solutions filtered by the composite membrane without electro-Fenton reaction were also significantly higher than those of the PVDF membrane, indicating that the water permeability and anti-pollutant adhesion properties of the composite membrane prepared in this example were also improved.

[0070] Escherichia coli and Staphylococcus aureus suspensions were prepared in the reactor to form a bacterial filtration system, and a constant current was connected and stirred continuously to examine the antibacterial ability of the composite membrane. The results showed that the PVDF membrane and the composite membrane without the electro-Fenton reaction had no antibacterial effect, and the composite membrane with the electro-Fenton reaction had an inactivation rate of 92.2% and 87.3% for Escherichia coli and Staphylococcus aureus, respectively, indicating that the composite membrane prepared in this example was non-toxic to microorganisms, but had a good antibacterial effect on both Gram-negative and Gram-positive bacteria when used as an electro-Fenton cathode.

[0071] The sludge-water mixture of anaerobic digested sludge was added into the reactor to form MBR, and a constant current was connected for continuous stirring to investigate the anti-pollution ability of the composite membrane during the long-term operation of the MBR. The results showed that after the start of the electro-Fenton reaction, the average pollution cycle of the composite membrane (34.2 d) was 2.1 times that of the PVDF membrane (16.0 d), indicating that the composite membrane prepared in this example degraded the adhered pollutants and inactivated the attached bacteria by producing ‧OH on its surface during the operation of the MBR, which alleviated the formation of biofilm on the membrane surface and the blockage of membrane pores, and significantly prolonged the membrane pollution cycle.

[0072] Embodiment 4:

[0073] A PVDF / rGO / Fe(Ⅱ) composite membrane as an electro-Fenton cathode comprises a substrate layer, an electro-Fenton active layer and a conductive layer arranged between the substrate layer and the electro-Fenton active layer, wherein the substrate layer is a polyvinylidene fluoride membrane, and the electro-Fenton active layer is a polyvinylidene fluoride membrane doped with siderite. The pore size of the electro-Fenton active layer is larger than that of the substrate layer. When the composite membrane is used as an electro-Fenton cathode under the action of electric current, H2O2 and ·OH are generated on the surface of the active layer to achieve membrane pollution control.

[0074] The preparation method of the PVDF / rGO / Fe(II) composite membrane comprises the following steps:

[0075] 1) Prepare PVDF membrane by phase inversion method, weigh 2 g / m 2 The rGO few layers of PVDF membrane were ultrasonically dispersed in deionized water for 30 min, and the rGO dispersion was filtered by suction using a PVDF membrane to cover the surface of the PVDF membrane with rGO, and then dried to obtain a PVDF / rGO double-layer membrane.

[0076] 2) After grinding and drying the siderite powder, 2.2 g of dry siderite powder with a particle size of 20-30 μm was screened and ultrasonically dispersed in 79.8 g of N, N-dimethylacetamide, 3 g of sodium dodecyl sulfate porogen and 15 g of PVDF were added, and heated and stirred to prepare a uniform casting solution;

[0077] 3) Using a scraper on a scraper machine, the casting liquid is coated on the rGO side of the PVDF / rGO double-layer membrane to a coating thickness of 100 μm to form a liquid film;

[0078] 4) The PVDF / rGO double-layer membrane coated with the liquid film was placed in the air for 5 s and then immersed in a water coagulation bath. After the membrane fell off, it was taken out and fully immersed in water. After natural air drying, a PVDF / rGO / Fe(Ⅱ) composite membrane was obtained.

[0079] The PVDF / rGO / Fe(Ⅱ) composite membrane as an electro-Fenton cathode is used in the inactivation of bacteria on the membrane surface and the degradation of organic matter on the membrane surface.

[0080] Embodiment 5:

[0081] A PVDF / rGO / Fe(Ⅱ) composite membrane as an electro-Fenton cathode comprises a substrate layer, an electro-Fenton active layer and a conductive layer arranged between the substrate layer and the electro-Fenton active layer, wherein the substrate layer is a polyvinylidene fluoride membrane, and the electro-Fenton active layer is a polyvinylidene fluoride membrane doped with siderite. The pore size of the electro-Fenton active layer is larger than that of the substrate layer. When the composite membrane is used as an electro-Fenton cathode under the action of electric current, H2O2 and ·OH are generated on the surface of the active layer to achieve membrane pollution control.

[0082] The preparation method of the PVDF / rGO / Fe(II) composite membrane comprises the following steps:

[0083] 1) Prepare PVDF membrane by phase inversion method, weigh 5 g / m 2 The single-layer rGO of the PVDF membrane was ultrasonically dispersed in deionized water for 55 min, and the rGO dispersion was suction filtered using a PVDF membrane to cover the surface of the PVDF membrane with rGO, and then dried to obtain a PVDF / rGO double-layer membrane;

[0084] 2) After grinding and drying the siderite powder, 2.8 g of siderite powder with a particle size of 20-60 μm was screened and ultrasonically dispersed in 77 g of N, N-dimethylacetamide, 3.5 g of propanol porogen and 16.7 g of PVDF were added, and heated and stirred to prepare a uniform film casting solution;

[0085] 3) Using a scraper on a scraper machine, the casting liquid is coated on the rGO side of the PVDF / rGO double-layer membrane to a coating thickness of 200 μm to form a liquid film;

[0086] 4) The PVDF / rGO double-layer membrane coated with the liquid film was placed in air for 15 s and then immersed in a water coagulation bath. After the membrane fell off, it was taken out and fully immersed in water. After natural air drying, a PVDF / rGO / Fe(Ⅱ) composite membrane was obtained.

[0087] The PVDF / rGO / Fe(Ⅱ) composite membrane as an electro-Fenton cathode is used in the inactivation of bacteria on the membrane surface and the degradation of organic matter on the membrane surface.

[0088] Embodiment 6:

[0089] A PVDF / rGO / Fe(Ⅱ) composite membrane as an electro-Fenton cathode, the composite membrane comprising a substrate layer, an electro-Fenton active layer and a conductive layer arranged between the substrate layer and the electro-Fenton active layer, the substrate layer being a polyvinylidene fluoride membrane, and the electro-Fenton active layer being a polyvinylidene fluoride membrane doped with siderite. The pore size of the electro-Fenton active layer is larger than that of the substrate layer. When the composite membrane is used as an electro-Fenton cathode under the action of electric current, H2O2 and ·OH are generated on the surface of the active layer to achieve membrane pollution control.

[0090] The preparation method of the PVDF / rGO / Fe(II) composite membrane comprises the following steps:

[0091] 1) Prepare PVDF membrane by phase inversion method, weigh 7 g / m 2 The rGO few layers of PVDF membrane were ultrasonically dispersed in deionized water for 60 min, and the rGO dispersion was suction filtered using a PVDF membrane to cover the membrane surface with rGO, and then dried to obtain a PVDF / rGO double-layer membrane.

[0092] 2) After grinding and drying the siderite powder, 2 g of siderite powder with a particle size of 20-40 μm was screened and ultrasonically dispersed in 76.3 g of N, N-dimethylacetamide, 4.7 g of polyvinyl pyrrolidone porogen and 17 g of PVDF were added, and heated and stirred to prepare a uniform casting solution;

[0093] 3) using a scraper on a scraper machine to apply the casting liquid to the rGO side of the PVDF / rGO double-layer membrane with a coating thickness of 160 μm to form a liquid film;

[0094] 4) The PVDF / rGO double-layer membrane coated with the liquid film was placed in air for 13 s and then immersed in a water coagulation bath. After the membrane fell off, it was taken out and fully immersed in water. After natural air drying, a PVDF / rGO / Fe(Ⅱ) composite membrane was obtained.

[0095] The PVDF / rGO / Fe(Ⅱ) composite membrane as an electro-Fenton cathode is used in the inactivation of bacteria on the membrane surface and the degradation of organic matter on the membrane surface.

[0096] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode, characterized in that: The invention comprises a substrate layer, an electro-Fenton active layer and a conductive layer arranged between the substrate layer and the electro-Fenton active layer, wherein the substrate layer comprises a polyvinylidene fluoride film, and the electro-Fenton active layer comprises a polyvinylidene fluoride film doped with siderite.

2. The PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode according to claim 1, characterized in that: The pore size of the electro-Fenton active layer is larger than that of the substrate layer.

3. The PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode according to claim 1, characterized in that: The conductive layer is a reduced graphene oxide film.

4. A method for preparing a PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode according to any one of claims 1 to 3, characterized in that: The steps include: 1) Dispersing reduced graphene oxide in deionized water, using a base membrane to filter the reduced graphene oxide dispersion by suction, so that the reduced graphene oxide is covered on the base membrane, and then drying to obtain a PVDF / rGO double-layer membrane; 2) ultrasonically dispersing siderite powder in an organic solvent, adding a porogen and polyvinylidene fluoride, and heating and stirring to obtain a film casting solution; 3) coating the vacuum degassing casting liquid on one side of the reduced graphene oxide of the PVDF / rGO double-layer membrane, letting it stand and then immersing it in a coagulation bath to solidify into a membrane, taking it out after the membrane falls off and soaking it in water, and obtaining the PVDF / rGO / Fe(Ⅱ) composite membrane after drying.

5. The method for preparing a PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode according to claim 4, characterized in that: The number of reduced graphene oxide layers is ≤5, and the amount of reduced graphene oxide added per unit area of ​​the substrate film is 2-10 g / m 2 .

6. The method for preparing a PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode according to claim 4, characterized in that: In step 2), the casting solution is prepared from the following components in parts by weight: 76-80 parts of organic solvent, 13-17 parts of polyvinylidene fluoride, 3-6 parts of porogen, and 2-3 parts of siderite powder.

7. The method for preparing a PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode according to claim 4, characterized in that: The polyvinylidene fluoride membrane is prepared by a phase inversion method, and has a pore size of 0.1-0.3 μm and a thickness of 100-200 μm.

8. The method for preparing a PVDF / rGO / Fe(II) composite membrane as an electro-Fenton cathode according to claim 4, characterized in that: In step 3), the coating thickness of the casting solution is 100-200 μm.

9. Use of the PVDF / rGO / Fe(II) composite membrane as claimed in any one of claims 1 to 3 as an electro-Fenton cathode in inactivating bacteria on the membrane surface and degrading organic matter on the membrane surface.

10. A membrane filtration reactor, characterized in that: The invention comprises the PVDF / rGO / Fe(II) composite membrane as an electric-Fenton cathode as described in any one of claims 1 to 3, wherein the PVDF / rGO / Fe(II) composite membrane as an electric-Fenton cathode is connected to the negative electrode of a DC power supply as an electric-Fenton cathode, and electric-Fenton anode materials are arranged in parallel on both sides of the electric-Fenton cathode, and the electric-Fenton anode materials are connected to the positive electrode of the power supply.

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